Conventionally, broadband light sources are used as a light source for a medical device or a spectroscopic analysis. Generally, halogen lamps are used as such a broadband light source, but are disadvantageous in that they are large in size, have a short life span, and are greatly affected by heat rays.
In contrast, LEDs and the like, which are semiconductor light emitting devices, are advantageous in that they are smaller in size and have a longer life span than halogen lamps, and they are capable of emitting light only in a specific wavelength range. The emitted light, however, has a short half width, namely about 50 nm.
In response to this, the present inventors have proposed a light source for an optical coherence tomography device including an infrared glass phosphor and a semiconductor light emitting device (see Patent Literature 1, Non-Patent Literature 1, 2, 3, and the like, for example). In a light source described in Patent Literature 1, the use of an infrared glass phosphor provides infrared light having a relatively long half width, namely 72 nm, 84 nm, and 88 nm.